Method of determining oil horizon permeability characteristics for a vertical drive gaseous pressurization secondary oil production method



Sept. 9, 1958 R. SPEAROW 2,851,104

METHOD OF DETERMINING OIL HORIZON PERMEABILITY CHARACTERISTICS FOR A VERTICAL DRIVE GASEOUS PRES Filed Feb. 2-. 1956 SURIZATION SECONDARY OIL PRODUCTION METHOD 2 Sheets-Sheet l INVENTOR.

' Ralph Spear-ow v BY Atto ey Sept. 9, 1958 R. SPEA METHOD OF DETERMINING OIL HORIZON FOR A VERTICAL DR IVE GASEO OIL PRODUC Filed Feb. 2, 1956 ROW PRESSURIZA PERMEABILITY CHARACTERISTICS TION SECONDARY N METHOD 2 Sheets-Sheet 2 INVENTOR. Ra/p/z Spear/ 0W United States atent O METHOD OF DETERMINKNG OIL HORIZON PER- MEABILITY CHARACTERISTICS FOR A VERTI- CAL DRIVE GASEOUS PRESSURIZATION SEC- ONDARY OIL PRODUCTION METHOD Ralph Spearow, Paola, Kans.

Application February 2, 1956, Serial No. 563,090

4 Claims. (Cl. 166-4) This invention relates to methods of determining the fluid permeability, both gas and liquid, of oil sands and refers more particularly to a method of determining the operating characteristics of an oil sand under a vertical drive gaseous pressurization oil production method.

Vertical drive gaseous pressurization secondary oil production I have shown in my issued patents, including No. 2,593,497, entitled Method and Apparatus for Producing an Oil Well, issued May 26, 1947; No. 2,725,106, entitled Oil Production issued December 20 1951; and No. 563,088, entitled, Oil Production Method (Movable Packer), issued February 2, 195 6 as well as in a number of pending applications, various operative modifications of a vertical drive gaseous pressurization oil production method, including my application Serial No. 563,089, filed February 2, 1956 entitled, Fracturing Packer Assembly and Method of Application Thereo The operating characteristics of such a method are several:

(1) A gaseous pressurization medium such as air or an i inert gas is forced into the top portion of an oil sand, preferably as close to the top as feasibly possible. This gas moves both vertically and horizontally in the top of the sand forming a gas cap or adding to any such cap already in the sand. As the gas cap expands, it drives the liquid oil before it through the sand. Core sections taken through sands pressurized under this method at various stages validate the fact that the gas scavenges the oil completely from the oil horizon. It is important that the gaseous pressurization area be as close to the top of the sand as possible so that all the oil is scavenged from the sand and a maximum vertical distance is provided between the gaseous pressurization area at the top of the sand and the oil withdrawal area at the bottom of the sand. The receptivity of an oil sand to gaseous pressurization at the top thereof depends upon the permeability of the sand at the well bore face at the pressurization input level. Sometimes it is desirable or necessary to fracture the face of the oil sand at the upper portion thereof in the pressurization area. Such fracturing increases the amount of pressurization medium which may be forced into the upper portion of the oil horizon per unit time at a given pressure. When an operator has a leasehold Which has many wells thereon in which he wishes to practice the vertical drive gaseous pressurization method, there is a serious problem involved in determining where to spot the pressurization Wells and determining how much pressure should be allocated to any given pressurization well in the total area. It is Well known that the permeability of an oil sand differs greatly at various points within itself. It is desirable, also, if possible, to uniformly pressurize a given sand over its entire area so that the oil withdrawal is uniform therefrom. It is also important to know how much pressure will be required to properly pressurize the sand to produce the oil therefrom in order to ascertain the size and type of pressurization equipment "ice which the operator will require. Therefore, it would be very valuable for an operator to have available data indicating the receptivity of an oil horizon to gaseous pressurization media in the pressurization well bores, before and after the well bores have been fractured and at various applied pressures.

(2) The second operating characteristic of my vertical drive gaseous pressurization oil production method is that liquid oil is withdrawn from the bottom portion of the oil sand or horizon preferably as close to the bottom as feasibly possible. The oil which is withdrawn in a secondary production method such as this has been driven downwardly by the previously described expanding gas cap produced by the gaseous pressurization of the top portion of the formation. I have previously set forth methods of well completion which permit finishing a well either as a combined pressurization and production well wherein gaseous pressure is put in at the top of the formation and oil withdrawn from the bottom of the formation in the same well bore or where separate pressurization and production wells are provided in separate well bores. Whichever method of completion is employed, it is evident that the oil withdrawal zone at the bottom portion of the oil horizon must be completely isolated from the gaseous pressurization input area at the top of the horizon. If the two zones are not sealed olf and isolated one from the other, when the gas cap contacts the production well bore the gaseous pressurization will immediately migrate down the open well bore without encountering anyv resistance to its flow and motion of the oil through the horizon will cease. I have previously set forth many methods of well completion which satisfactorily seal off and isolate these areas, one from the other. The oil production zones at the bottom of the horizon from which sealed tubings or casings draw fluid oil are preferably as close to the bottom of the horizon as possible to permit as complete production of the liquid oil from the formation as possible, since as soon as the lower edge of the expanding gas cap reaches the boundary of the oil production area in the production well borehole, the production well is through as a producer for the gaseous pressure medium from the pressurization area will immediately recycle up through the production casing without producing oil, following the line of least resistance.

It is obvious that it would be desirable for the operator to know the productive potential of a given Well or a given sand in a given land area under certain pressures. It is well known that oil sands vary greatly in their permeability one from the other and that a given oil sand varies greatly in its own permeability from point to point. Sometimes it is desirable to fracture the oil production zone so that greater production therefrom will be possible. Should the operator know the productive capacity of a given well in its cross-sectional production area he could evaluate whether or not to drill other wells in the close vicinity, fracture the horizon or increase the pressurization in that vicinity. Thus, information as to the permeability of the oil production zone at the bottom part of the sand is of prime importance in the operation of a vertical drive gaseous pressurization method such as has been described.

(3) The third operating characteristic of my vertical drive gaseous pressurization method has been mentioned in part before, namely, the absolute necessity of sealing the pressurization input well above the oil horizon so that the gaseous pressurization media will not leak into the overlying formations above the oil sand and sealing the well bore of the production well above the oil production zone at the bottom of the horizon so that the gaseous pressurization media cannot move directly from the gaseous pressure input area to the liquid oil production General on oil well permeability An earthern oil reservoir is usually a porous rock formation in which the pores in the rock are connected by very small passageways, often microscopic in size, and the size and shape of these minute passageways, together with the physical characteristics of the oil stored therein, determine both the volume of oil that will move through these passageways in any given time interval under any given pressure and the degree of pressure required to move any given volume of oil in any stated time interval.

I have determined by experiment the fact that oil will move in any direction through the pores and connecting passageways in an oil reservoir rock, or the reverse of that direction, when the pressure applied is the same for both directions under test. This conclusion is determined by actual well bore pressurization experiments and also is more or less self-evident from the simple fact that there are no one-way valves positioned in the pores or passageways in the oil reservoir rock or sand.

Heretofore, in estimating oil sand permeability and productivity, it has been necessary to rely upon the analyses of core samples taken from an oil reservoir wherein the internal permeability of the samples analyzed is set forth and the movement of the oil resident in the reservoir as related to the pressures existent in the reservoir is extrapolated from the core sample data. This is at best only relatively accurate. The inaccuracy factor in such analyses arises largely from the well-known fact that the permeability characteristics of an oil reservoir often change radically within relatively short distances, sometimes within a few inches. Thus the permeability of a core sample of the reservoir rock, taken from the center of a core hole through the reservoir rock, does not necessarily reflect the permeability characteristics of the reservoir rock as little as a few inches away from the well bore.

Distances between wells in any oil field are usually several hundred feet and the permeability character of the reservoir rock between well bores can only be approximated. Since the final factor in determining oil production volumes at any given pressure level in the reservoir is the permeability of the reservoir to the passage of oil through the reservoir rock, such conventional core analyses, by themselves, are highly inadequate for the exact predictions desired of productivity volumes relative existent pressures or pressures to be superimposed.

When an oil field which was abandoned at the end of the flowing and pumping period (primary period of production) is considered for secondary production operations, one of the most important elements entering cost figures for surface installation is the form and size of the plant which must deliver the secondary pressurizing agent to the oil reservoir. When the over-all size of the field is known, the question then to be answered is, how much pressure must be established in the oil reservoir to produce a stated volume of oil production per day? When that question has been answered for the oil production operator, he can then calculate what his surface compression plantwill cost and the time it will require to reach a desired degree of pressurization in the oil reservoir.

It is also desirable, in some instances, to apply extra pressure to fields still under partial pressure (fields in which the reservoir pressure is lower than at the date of field discovery). In such instance, the operator desires to rebuild the reservoir pressure sufliciently to deliver a desired daily volume of oil. It would be desirable in such instance also to be able to calculate the degree of pressure required to meet the desires relative production volumes and the kind and size of pressurization equipment demanded.

The present inventive method involves testing the Oi horizon under conditions of reverse flow of fluids into the horizon. It should be kept in mind that reverse flow must, in all movement characteristics, duplicate the behavior of the oil as it flows from the reservoir into the well bores. Thus, in oil production, the oil reservoir delivers whatever oil is delivered to the well bore in a more or less steady flow due to the uniformity of the pressure distribution throughout the oil reservoir and this steadiness of flow from the reservoir to the well bore is interrupted only by the behavior of the expanding gases in the oil after they reach the well bore.

Therefore, an object of the present invention is to provide a method of determining the fluid permeability, both gas and liquid, of oil sands.

Another object of the invention is to provide a method of predetermining the operating characteristics of an oil sand under a vertical drive gaseous pressurization oil production method.

Another object of the invention is to provide a method of predetermining the operating characteristics of an oil sand under a vertical drive gaseous pressurization oil production method wherein the receptivity of the top portion of the oil sand to gaseous pressurization media is established and the productive capacity of the lower portion of the oil sand is determined for fluid oil.

Another object of the invention is to provide a method of predetermining the operating characteristics of an oil sand under a vertical drive gaseous pressurization method wherein either the top or bottom portion of the horizon is fractured or both to increase the receptivity to gaseous pressurization media or oil productivity, respectively.

Another object of the invention is to provide a method of determining the fluid permeability, both gas and liquid, of an oil sand under varying fluid pressures, both gas and liquid, whether or not the oil sand has been fractured.

Another object of the invention is to provide a method of determining the fluid permeability, both gas and liquid, of an oil sand in a limited or restricted area, particularly in the instance where a limited portion of the top level of the oil horizon is to be used for gaseous pressurization and where a limited portion of the lower level of the oil horizon is to be used for the production of fluid oil.

Other and further objects of the invention will appear in the course of the following description.

In the drawings which form a part of the instant specification and which are to be read in conjunction therewith, there is shown two modifications of the invention and, in the various views, like numerals are employed to indicate like parts.

Fig. 1 is a cross-sectional view through an earth formation containing an oil horizon with the well bore of a well drilled therethrough and apparatus for practicing one modification of the invention shown schematically positioned on the ground surface.

Fig. 2 is a cross-sectional view through an earth forma tion containing an oil horizon with the well bore of an oil well drilled therethrough, a second modification of the apparatus for practicing the invention being positioned on the ground surface and shown schematically in the figure.

Referring first to Fig. 1, the numeral 10 designates a power generating unit such as an electric motor or internal combustion engine, which is of sufiicient horsepower to properly operate the air or gas compressor 11. 12 shows the belt which transmits power from the engine or motor 10 to gas compressor 11. Such belt 12 may be eliminated if the power is directly connected to the compressor from the power generating unit. 13 is a compressed air or gas vessel of sufiicient volume and pressure holding strength to deliver the required pressures to the liquid holding vessel 14. Pipe 15 carries compressed air or gas from the compressor 11 to the vessel 13. Adjustable safety valve 16 prevents the pressure in vessel 13 going above any predetermined figure. Valve 17 controls the flow of fluid between compressor 11 and vessel 13. Pipe 18 carries compressed air or gas from vessel 13 to fluid oil or liquid oil vessel 14. Adjustable pressure regulator 19 is positioned in line 18. Valve 20 is also in line 18. Pressure gauges 21 and 22 are fixed to vessels 13 and 14, respectively. Fluid sight gauge 23 shows the fluid level in vessel 14 at any time interval or instant between the fluid levels in vessel 14 which are indicated by the dotted lines marked a and b. 24 indicates the fluid oil entrance port to the vessel 14. Flow line 25 delivers liquid from vessel 14 to the well head. Union 26 in line 25 permits speedy connection, thus making the truck mounted apparatus movable from wellhead to wellhead. Drain vent 27 serves to drain tank or vessel 14, and has valve 28 therein. Drain valve 29 on vessel 13 serves to lead 011 any condensates that might form therein. Union 30, also on line 25, is also for high speed connection. High pressure swing connections 31 and 32 permit connecting of line 25 to the wellhead. High pressure valve 33 permits disconnecting of the truck apparatus from the wellhead at the end of the test.

The apparatus previously described is designed to provide a measure of the liquid productivity of an oil sand at any cross section thereof. It is particularly adapted for determining the liquid productivity of an oil sand at the bottom thereof, such determination is extremely valuable in a vertical drive gaseous pressurization method as above described. It is also often desirable (referring to original production) to be able to discover the levels in an oil sand which have the greatest permeability so that if it is desired to fracture any given level in the sand the most permeable part thereof may be determined and isolated and packed off for fracturing. Also, if it is desired to ascertain the productivity of the whole crosssectional face of an oil sand at a given pressure this method is applicable thereto. Such latter information would not be desired in a vertical drive gaseous pressurization method but might be useful in a horizontal drive liquid or water drive production method in secondary production.

Referring to the drawing, the situation will be first considered where it is desired to test the oil productivity of a limited cross-sectional area of an oil sand. Preferably, this method is to be applied to the lower portion of an oil horizon for use in a vertical gaseous drive pressurization method but the method, as to be described, is applicable to any portion of the oil horizon. The main problem is to isolate the predetermined cross section of the well bore face and then apply the liquid pressure only to that predetermined portion. In the drawing is shown a preferred method of doing this. The fracturing packer assembly shown in my application, Serial No. 563,089 entitled, Fracturing Packer Assembly is also feasible for use in this method. The borehole 34 of a well is drilled to the vicinity of the bottom or the bottom of the oil horizon. A casing or production tubing 35 is run to the bottom of the borehole and sealed to the well wall from the bottom of the casing to a level above the top of the oil sand as shown at 36 by an annular column of sealing substance or cement. The casing is then perforated as shown at 37 at the level of the horizon desired to be tested for productivity. These perforations 37 are preferably as close to the bottom of the horizon as possible for the optimum working of the vertical drive gaseous pressurization method. Casing 35 has sealed top portion 38 with pressure valve 39 thereon and flow line 40 attached thereto. Several rows of perforations may be made vertically in the casing 35 and its surrounding annular seal 36 if desired. This gives any desired cross-sectional area for the pressurization. It should be also noted that before the running of the casing 35 and sealing thereof to the well bore Wall the face of the horizon may be fractured as shown at 41. After perforating, the well is ready for the test. The apparatus on the truck 42 carried by wheels 43 is connected by means of the unions 26 and 30 and swing connections 31 and 32.

Oil of the exact and same character as that contained in the oil reservoir 44, in fact preferably taken from storage oil already produced from said reservoir, is then placed in vessel 14 to fill it to the upper dotted line marked a. The distance from the surface valve 33 on wellhead 35 down to the perforations 37 at the base of the oil reservoir 46 is known. Known also is the exact column weight of the oil, expressed in pounds per square inch for that depth. The casing 35 is filled with oil from storage from the bottom of the well to the valve 12. Vessel 14 and all lines leading from it to the wellhead 35 are bled of all air or other gas and they are then filled with oil of the same character as is placed in casing 35 and vessel 14.

The motive power 10 is then started and compressed air or gas is fed from compressor 11 to vessel 13 after opening valve 17. Valve 20 leading from vessel 13 to liquid vessel 14 remains closed until the pressure in the vessel 13 reaches the desired degree as shown by the action of pressure release valve 16. At this point, valve 20 from vessel 13 to vessel 14 is opened and gaseous pressurization media is fed through that line and pressure regulator 19 therein to vessel 14 until the pressure on gauge 22 on vessel 14 reaches the desired and predetermined level.

At this point, valve 33 is opened and the pressure in the top of vessel 14 is permitted to push oil into the casing 35 and thus into the oil reservoir through perforations 37 (and fracture 41 if it exists). This oil will distribute itself into the reservoir 46 in exactly that pattern of distribution that represents the pattern of oil delivery which will operate under reverse flow when the oil is moving in like volume and under like pressure from the reservoir into the well bore. If the pressure in vessel 14 does not prove sufiicient to satisfy the volume requirement, then added pressure may be provided by changing the set of regulator 19 until the desired degree of pressure is produced. The lowering of the oil fluid in vessel 14 as seen in sight gauge 23 in any given time interval gives the operator the answer as to how much oil will move in the reservoir rock pores and connecting passageways under any selected pressure for the given cross-sectional area being pressurized.

It is obvious that to obtain at the surface the same volume of oil from the reservoir that was sent into the reservoir in the practice of the method as above described, the pressure to be established in the reservoir pores will always be equal to the pressure registered on the pressure gauges 39 and 22 on the wellhead and vessel 14 plus twice the weight of the fluid column of oil extending from the valve 33 to the perforations 37. Thus, for example, if pressure on the surface gauges 39 and 22 register at 200 p. s. i. g. and if the weight of the fluid column of oil from the valve 12 to perforations 18 is 400 pounds per square inch, and if the amount of oil forced into the reservoir 46 under such conditions is ten barrels per hour, it is concluded that, in actual oil production, if 1000 pounds pressure is established in oil reservoir 41, this well will flow at the rate of ten barrels per hour. The latter figure is, of course, applicable only as long as the reservoir pressure is maintained at 1000 p. s. i. g. and there is oil in the reservoir above the perforations 37 It also should be noted that the pressure applied to the top of the fluid column must be steady and not pulsating for the amount of fluid measured over a unit of time to be any index of the permeability of the horizon.

Referring to Fig. 2, therein is shown apparatus for testing both the liquid productivity of a section of an oil horizon and the receptivity of a limited portion of the horizon to input of gaseous pressurization media. At 45 is shown an air compressor having drive shaft 46 with drive belt receiving wheel 47 thereon. 48 is the input for a line from another like air compressor if a series of stages of compressors should be desired. Safety valve 49 is provided at the top of said input line 48. Line carries compressed air or gas from compressor 45 through fitting 51 into air tank 52. Air tank 52 has pressure gauge 53, safety valve 54 on the top thereof and drainage line 55 with valve 56 therein at the bottom thereof for draining off any condensates from the vessel. Line 57 takes compressed air from reservoir tank 52 and T 58 has lower air flow line 59 leading therefrom with union 60 and valve 61 therein and gas measuring meter 62 further along therein in a line extension 63 leading to the wellhead. Valves 64 and unions 65 and 66 are also in said air line to the wellhead. Secondary air line 67 from T 58 has valve 68, union 69, pressure regulator 70 and union 71 thereon and leads into liquid oil containing tank 72. Oil tank 72 has input opening 73 at the top thereof, pressure gauge 74 also at the top thereof, sight gauge 75 at the side thereof to indicate the fluid level therein and drainage vent 76 with valve 77 therein at the bottom. Line 76 leads into T 78 below the oil tank with one arm of the T going to drainage and the other a fluid line 79 to the well. Line 79 has union 80, valve 81 and liquid meter 82 therein. Valve 83 and union 84 are on the downflow side of the meter, the line 79 then leading into T 85 and common line 86 having union 87 therein leading to the wellhead. Swing fittings 88 and 89 lead to line 90 into the wellhead having valve 91 thereon. The whole pressurization assembly is carried by deck 92 mounted on wheels 93.

The operation of the unit to force liquid oil into the oil horizon is essentially the same as that previously described relative the apparatus in Fig. 1. In this instance, however, the valve 61 on the air line 59 must be shut off, the valve 68 on the air line 67 between air tank 52 and oil tank 72 opened, the valves 81 and 83 on the line 79 to the common line 86 leading from the oil tank to the wellhead opened and the valve 64 on the air line after the gas measuring meter closed. In this manner, assuming well bore 94 drilled to the bottom of the oil sand, the horizon 95 fractured at the vicinity of the bottom of the horizon as shown at 96 and/or at the top of the horizon as shown at 97, the casing 98 run to the bottom of the borehole and sealed 99 to the Well wall from the bottom of the horizon to a level above the bottom of the horizon and the casing and its surrounding seal perforated at the bottom of the horizon 100 and/ or at the top of the horizon 101 opposite the fractures 96 and 97, the casing 98 having sealed portion 102 at the top end thereof with pressure gauge 103 thereon, the method will be applied.

The method to measure liquid oil productivity at the bottom of the horizon will first be described, assuming that the casing has been perforated and fractured only at the bottom of the horizon. Oil of the character previously described is taken from storage oil and placed in vessel 72 to fill it to any given level on the sight gauge. The casing 98 is filled with oil from storage from the bottom of the well to the valve 91. The vessel or oil tank 72 and all lines leading from it to the wellhead 98 are bled of air or other gas and filled with oil of the same character as described. The compressor 45 is started and compressed air or gas is fed from the compressor 45 to air tank 52. The valves 61 and 68 on the air lines remain closed until the pressure in the air tank reaches the desired degree as shown by the action of the pressure release valve 54 and gauge 53 on the top of the air tank. At this time the valve- 68 above the T 58 is opened, the valve 61 below the T remaining closed and the pressurization media is fed through line 67 and regulator 70 therein into the oil tank 72 until the pressure on the gauge 74 on oil tank 72 reaches the desired and predetermined level. At this point, valves 81, 83 and 91 are opened (64 being closed) and the pressure in the top of the oil tank 72 is permitted to push the oil through the fluid meter 82 and lines 76, 79, 86 and 99 into the oil reservoir through the lower perforations 100 and fracture 96. The oil distributes itself into the reservoir in exactly that pattern of distribution that represents the pattern of oil delivery that would operate under reverse flow when the oil would move in like volume under like pressure from the reservoir into the well bore. If the pressure in the vessel 72 does not prove sufficient to satisfy the volume requirements, then added pressure is provided by changing the set of regulator 70 until that degree of pressure is achieved. The lowering of the fluid oil as seen in the sight gauge 75 in any given time period gives the operator the answer as to how much oil will move in the reservoir rock pores and connecting passageways under any selected pressure. Meter 82 also can furnish this information or a check thereon.

Now, considering the process of determining the receptivity of the oil horizon at any portion thereof (but preferably at the top portion) to input of gaseous pressurization media at any given pressure, the upper valve 68 on line 67 is closed as is valve 83. After the desired pressurization has been built up in the air tank 52, valve 61 is opened and air pressure is forced through regulating and measuring meter 62 and open valves 64 and 91 into the wellhead. Since the air or gas is compressible where the liquid oil is not, it is obvious that pressure must be built up within the sealed casing and lines between the wellhead and the air tank sufficient to move the gaseous pressurization media out into the horizon. The operator selects the desired pressure he wishes to exert on the well bore face and sets the regulator meter 70 to maintain such pressure. When the amount of gas accepted by the well bore has stabilized from the initial high receptivity required to fill the well bore, the quantity of pressurization media accepted by the well bore face per unit time at a given pressure may be determined.

It is evident that the selected pressures utilized in both the liquid pressurization of the face and the gaseous pressurization of the face may be set at any predetermined values or set at a series of predetermined values to ascertain the acceptance rates of the oil horizon. It is also obvious that the Wells tested may be completed in a number of ways to isolate the crosssectional areas of the oil horizon to be tested. Only one such way has been shown in the application as a specific example. My issued patents and previous applications show many other ways such as (l) gravel packing around a perforated casing and then sealing above the gravel packed area or (2) packing off a casing against the well bore face and then optionally putting in a sealing column above the packer for any desired distance. The essence of the method is that a predetermined cross-sectional area of the well bore face is isolated and connected with a fluid pressurization channel to the surface. The pressure on the fluid in the channel is then raised to a predetermined level and the acceptance ratio per unit time at a given pressure is measured.

Fromthe foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the invention.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter hereinabove set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim:

1. A method of determining the oil productivity of a limited portion of an oil horizon comprising the steps of drilling the bore hole of a well at least slightly below the portion of the oil horizon to be tested, sealing off a limited zone within the oil horizon in said bore hole from which it is contemplated to produce oil, applying liquid of a character similar to that contained in the oil horizon under pressure only to the well bore face in said limited zone, measuring the amount of said liquid accepted by the Well bore face in said limited zone per unit time at a given pressure, and subsequently producing oil from said limited zone when the measured liquid acceptance of said zone indicates the production from said zone would be economically satisfactory.

2. A method of determining the oil well productivity of a limited portion of an oil horizon comprising the steps of drilling a well bore below the portion of the oil horizon to be tested, sealing off a limited zone within the oil horizon in said bore hole from which it is contemplated to produce oil, applying liquid of a character similar to that contained in the oil sand under pressure only to the well bore face in the said limited zone, measuring the amount of said liquid accepted by the well bore face in said limited zone per unit time at a given pressure and subsequently fracturing the well bore face in the said limited zone when the measured liquid acceptance of said zone indicates the production from said area without fracturing would be uneconomically low.

3. A method of determining the oil productivity of a limited portion of an oil horizon comprising the steps of drilling a well bore below the portion of the oil horizon to be tested, sealing off a limited zone within the oil horizon in said bore hole from which it is contemplated to produce oil, applying liquid of a character similar to that contained in the oil horizon under pressure only to the well bore face in the said limited zone, measuring the amount of the said liquid accepted by the well bore face in said limited zone per unit time at a given pressure, and,

when the measured liquid acceptance of said area indicates the productivity from said area would be uneconom ically low, subsequently sealing off a second limited zone within the oil horizon from which it is contemplated to produce oil, and applying liquid of a character similar to that contained in the oil horizon under pressure only to the well bore face in the said second limited zone and measuring the amount of liquid accepted by the well bore face per unit time at a given pressure.

4. A method of determining the oil productivity of a limited portion of an oil horizon comprising the steps of drilling a well bore below the portion of the oil horizon to be tested, sealing 01f a limited zone within the oil horizon in said bore hole from which it is contemplated to produce oil, applying liquid of a character similar to that contained in the oil horizon under pressure only to the Well bore face in the said limited zone, measuring the amount of said liquid accepted by the well bore face in said limited zone per unit time at a given pressure, and, when the measured liquid acceptance of said zone indicates the productivity from said zone would be uneconomically low, repeating the previous steps to further limited zones of the horizon from which it is contemplated to produce until a limited zone is found from which production will be economically satisfactory.

References Cited in the file of this patent UNITED STATES PATENTS 2,352,834 Hassler July 4, 1944 2,725,106 Spearow Nov. 29, 1955 2,754,911 Spearow July 17, 1956 

